LPCSTR LPCTSTR and LPTSTR

Question

What the difference between LPCSTR  LPCTSTR and LPTSTR   Why do we need to do this to convert a string into a LV    ITEM structure variable pszText     LV DISPINFO dispinfo    dispinfo item pszText   LPTSTR  LPCTSTR string

User · Answer

Adding to John and Tim s answer   Unless you are coding for Win98  there are only two of the 6  string types you should be using in your application   LPWSTR LPCWSTR   The rest are meant to support ANSI platforms or dual compilations   Those are not as relevant today as they used to be

User · Answer

Quick and dirty   LP    Long Pointer   Just think pointer or char   C   Const  in this case  I think they mean the character string is a const  not the pointer being const     STR is string  the T is for a wide character or char  TCHAR  depending on compile options

User · Answer

To answer the first part of your question   LPCSTR is a pointer to a const string  LP means Long Pointer   LPCTSTR is a pointer to a const TCHAR string   TCHAR being either a wide char or char depending on whether UNICODE is defined in your project   LPTSTR is a pointer to a  non-const  TCHAR string  In practice when talking about these in the past  we ve left out the  pointer to a  phrase for simplicity  but as mentioned by lightness-races-in-orbit they are all pointers   This is a great codeproject article describing C   strings  see 2 3 the way down for a chart comparing the different types

User · Answer

Adding to John and Tim s answer   Unless you are coding for Win98  there are only two of the 6  string types you should be using in your application   LPWSTR LPCWSTR   The rest are meant to support ANSI platforms or dual compilations   Those are not as relevant today as they used to be

User · Answer

Quick and dirty   LP    Long Pointer   Just think pointer or char   C   Const  in this case  I think they mean the character string is a const  not the pointer being const     STR is string  the T is for a wide character or char  TCHAR  depending on compile options

User · Answer

The short answer to 2nd part of the question is simply that CString class doesn t provide a direct typecast conversion by design and what you are doing is kind of cheat  A longer answer is the following  The reason you can typcast CString to LPCTSTR is because CString provides this facility by overriding operator   By design it provides conversion to only LPCTSTR pointer so the string value can t be modified with this pointer  In other words  it simply doesn t provide an overload operator  to convert the CString into LPSTR for the same reason as above  They don t want to allow altering the string value this way  So essentially  the trick is to use the operator CString provide and get this  LPTSTR lptstr    LPCTSTR  string     CString provide this operator overload  Now LPTSTR can be further type casted to LPSTR    dispinfo item pszText   LPTSTR  lpfzfd      accomplish the cheat  P  The correct way to get LPTSTR from  CString  is this though  complete example   CString str    T  quot Hello quot    LPTSTR lpstr   str GetBuffer str GetAllocLength     str ReleaseBuffer       you must call this function if you change the string above with the pointer  Again because the GetBuffer   returns LPTSTR for that reason that now  you can modify

User · Answer

The short answer to 2nd part of the question is simply that CString class doesn t provide a direct typecast conversion by design and what you are doing is kind of cheat  A longer answer is the following  The reason you can typcast CString to LPCTSTR is because CString provides this facility by overriding operator   By design it provides conversion to only LPCTSTR pointer so the string value can t be modified with this pointer  In other words  it simply doesn t provide an overload operator  to convert the CString into LPSTR for the same reason as above  They don t want to allow altering the string value this way  So essentially  the trick is to use the operator CString provide and get this  LPTSTR lptstr    LPCTSTR  string     CString provide this operator overload  Now LPTSTR can be further type casted to LPSTR    dispinfo item pszText   LPTSTR  lpfzfd      accomplish the cheat  P  The correct way to get LPTSTR from  CString  is this though  complete example   CString str    T  quot Hello quot    LPTSTR lpstr   str GetBuffer str GetAllocLength     str ReleaseBuffer       you must call this function if you change the string above with the pointer  Again because the GetBuffer   returns LPTSTR for that reason that now  you can modify

User · Answer

To answer the first part of your question   LPCSTR is a pointer to a const string  LP means Long Pointer   LPCTSTR is a pointer to a const TCHAR string   TCHAR being either a wide char or char depending on whether UNICODE is defined in your project   LPTSTR is a pointer to a  non-const  TCHAR string  In practice when talking about these in the past  we ve left out the  pointer to a  phrase for simplicity  but as mentioned by lightness-races-in-orbit they are all pointers   This is a great codeproject article describing C   strings  see 2 3 the way down for a chart comparing the different types

User · Answer

To answer the first part of your question   LPCSTR is a pointer to a const string  LP means Long Pointer   LPCTSTR is a pointer to a const TCHAR string   TCHAR being either a wide char or char depending on whether UNICODE is defined in your project   LPTSTR is a pointer to a  non-const  TCHAR string  In practice when talking about these in the past  we ve left out the  pointer to a  phrase for simplicity  but as mentioned by lightness-races-in-orbit they are all pointers   This is a great codeproject article describing C   strings  see 2 3 the way down for a chart comparing the different types

User · Answer

To answer the second part of your question  you need to do things like  LV DISPINFO dispinfo    dispinfo item pszText   LPTSTR  LPCTSTR string     because MS s LVITEM struct has an LPTSTR  i e  a mutable T-string pointer  not an LPCTSTR  What you are doing is  1  convert string  a CString at a guess  into an LPCTSTR  which in practise means getting the address of its character buffer as a read-only pointer   2  convert that read-only pointer into a writeable pointer by casting away its const-ness   It depends what dispinfo is used for whether or not there is a chance that your ListView call will end up trying to write through that pszText  If it does  this is a potentially very bad thing  after all you were given a read-only pointer and then decided to treat it as writeable  maybe there is a reason it was read-only   If it is a CString you are working with you have the option to use string GetBuffer   -- that deliberately gives you a writeable LPTSTR  You then have to remember to call ReleaseBuffer   if the string does get changed  Or you can allocate a local temporary buffer and copy the string into there   99  of the time this will be unnecessary and treating the LPCTSTR as an LPTSTR will work    but one day  when you least expect it

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8-bit AnsiStrings  char  8-bit character  underlying C C   data type  CHAR  alias of char  Windows data type  LPSTR  null-terminated string of CHAR  Long Pointer  LPCSTR  constant null-terminated string of CHAR  Long Pointer Constant   16-bit UnicodeStrings  wchar t  16-bit character  underlying C C   data type  WCHAR  alias of wchar t  Windows data type  LPWSTR  null-terminated string of WCHAR  Long Pointer  LPCWSTR  constant null-terminated string of WCHAR  Long Pointer Constant   depending on UNICODE define  TCHAR  alias of WCHAR if UNICODE is defined  otherwise CHAR LPTSTR  null-terminated string of TCHAR  Long Pointer  LPCTSTR  constant null-terminated string of TCHAR  Long Pointer Constant   So      Item 8-bit  Ansi  16-bit  Wide  Varies     character CHAR WCHAR TCHAR   string LPSTR LPWSTR LPTSTR   string  const  LPCSTR LPCWSTR LPCTSTR    Bonus Reading TCHAR   Text Char  archive is   Why is the default 8-bit codepage called  quot ANSI quot   From Unicode and Windows XP by Cathy Wissink Program Manager  Windows Globalization Microsoft Corporation May 2002  Despite the underlying Unicode support on Windows NT 3 1  code page support continued to be necessary for many of the higher-level applications and components included in the system  explaining the pervasive use of the    A     ANSI  versions of the Win32 APIs rather than the    W        wide    or Unicode  versions   The term    ANSI    as used to signify Windows code pages is a historical reference  but is nowadays a misnomer that continues to persist in the Windows community  The source of this comes from the fact that the Windows code page 1252 was originally based on an ANSI draft  which became ISO Standard 8859-1  However  in adding code points to the range reserved for control codes in the ISO standard  the Windows code page 1252 and subsequent Windows code pages originally based on the ISO 8859-x series deviated from ISO  To this day  it is not uncommon to have the development community  both within and outside of Microsoft  confuse the 8859-1 code page with Windows 1252  as well as see    ANSI    or    A    used to signify Windows code page support

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8-bit AnsiStrings  char  8-bit character  underlying C C   data type  CHAR  alias of char  Windows data type  LPSTR  null-terminated string of CHAR  Long Pointer  LPCSTR  constant null-terminated string of CHAR  Long Pointer Constant   16-bit UnicodeStrings  wchar t  16-bit character  underlying C C   data type  WCHAR  alias of wchar t  Windows data type  LPWSTR  null-terminated string of WCHAR  Long Pointer  LPCWSTR  constant null-terminated string of WCHAR  Long Pointer Constant   depending on UNICODE define  TCHAR  alias of WCHAR if UNICODE is defined  otherwise CHAR LPTSTR  null-terminated string of TCHAR  Long Pointer  LPCTSTR  constant null-terminated string of TCHAR  Long Pointer Constant   So      Item 8-bit  Ansi  16-bit  Wide  Varies     character CHAR WCHAR TCHAR   string LPSTR LPWSTR LPTSTR   string  const  LPCSTR LPCWSTR LPCTSTR    Bonus Reading TCHAR   Text Char  archive is   Why is the default 8-bit codepage called  quot ANSI quot   From Unicode and Windows XP by Cathy Wissink Program Manager  Windows Globalization Microsoft Corporation May 2002  Despite the underlying Unicode support on Windows NT 3 1  code page support continued to be necessary for many of the higher-level applications and components included in the system  explaining the pervasive use of the    A     ANSI  versions of the Win32 APIs rather than the    W        wide    or Unicode  versions   The term    ANSI    as used to signify Windows code pages is a historical reference  but is nowadays a misnomer that continues to persist in the Windows community  The source of this comes from the fact that the Windows code page 1252 was originally based on an ANSI draft  which became ISO Standard 8859-1  However  in adding code points to the range reserved for control codes in the ISO standard  the Windows code page 1252 and subsequent Windows code pages originally based on the ISO 8859-x series deviated from ISO  To this day  it is not uncommon to have the development community  both within and outside of Microsoft  confuse the 8859-1 code page with Windows 1252  as well as see    ANSI    or    A    used to signify Windows code page support

User · Answer

Adding to John and Tim s answer   Unless you are coding for Win98  there are only two of the 6  string types you should be using in your application   LPWSTR LPCWSTR   The rest are meant to support ANSI platforms or dual compilations   Those are not as relevant today as they used to be

User · Answer

Quick and dirty   LP    Long Pointer   Just think pointer or char   C   Const  in this case  I think they mean the character string is a const  not the pointer being const     STR is string  the T is for a wide character or char  TCHAR  depending on compile options

User · Answer

Adding to John and Tim s answer   Unless you are coding for Win98  there are only two of the 6  string types you should be using in your application   LPWSTR LPCWSTR   The rest are meant to support ANSI platforms or dual compilations   Those are not as relevant today as they used to be

User · Answer

To answer the first part of your question   LPCSTR is a pointer to a const string  LP means Long Pointer   LPCTSTR is a pointer to a const TCHAR string   TCHAR being either a wide char or char depending on whether UNICODE is defined in your project   LPTSTR is a pointer to a  non-const  TCHAR string  In practice when talking about these in the past  we ve left out the  pointer to a  phrase for simplicity  but as mentioned by lightness-races-in-orbit they are all pointers   This is a great codeproject article describing C   strings  see 2 3 the way down for a chart comparing the different types

User · Answer

Quick and dirty   LP    Long Pointer   Just think pointer or char   C   Const  in this case  I think they mean the character string is a const  not the pointer being const     STR is string  the T is for a wide character or char  TCHAR  depending on compile options

User · Answer

To answer the second part of your question  you need to do things like  LV DISPINFO dispinfo    dispinfo item pszText   LPTSTR  LPCTSTR string     because MS s LVITEM struct has an LPTSTR  i e  a mutable T-string pointer  not an LPCTSTR  What you are doing is  1  convert string  a CString at a guess  into an LPCTSTR  which in practise means getting the address of its character buffer as a read-only pointer   2  convert that read-only pointer into a writeable pointer by casting away its const-ness   It depends what dispinfo is used for whether or not there is a chance that your ListView call will end up trying to write through that pszText  If it does  this is a potentially very bad thing  after all you were given a read-only pointer and then decided to treat it as writeable  maybe there is a reason it was read-only   If it is a CString you are working with you have the option to use string GetBuffer   -- that deliberately gives you a writeable LPTSTR  You then have to remember to call ReleaseBuffer   if the string does get changed  Or you can allocate a local temporary buffer and copy the string into there   99  of the time this will be unnecessary and treating the LPCTSTR as an LPTSTR will work    but one day  when you least expect it

[c++] LPCSTR, LPCTSTR and LPTSTR

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